Drill screw with swaging threads



April 21, 1970 RQL. THURSTON 3,507,183

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April 21, 1970 R. L. THURSTON 3,507,183

DRILL SCREW WITH SWAGING THREADS Filed Jan. 25, 1969 2 Sheets-Sheet 2 INVENTOR.

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United States Patent 3,507,183 DRILL SCREW WITH SWAGING THREADS Raymond L. Thurston, Dearborn, Mich., assignor to Microdot Inc., New York, N.Y., a corporation of California Filed Jan. 23, 1969, Ser. No. 793,259 Int. Cl. B21h 3/04; B23g 7/02; B21k /04;

F16b 25/00, 33/02 US. CI. 85-47 5 Claims ABSTRACT OF THE DISCLOSURE A thread swaging screw has a body formed from a section of wire with a driving head at one end and a tap red section and drill on the opposite end containing flutes which extend into a rolled thread on the tapered section and body. The forward faces of the thread sections extend into the flutes to swage rather than out a thread in the wall of the drilled hole.

BACKGROUND OF THE INVENTION From a search the following patents were selected to show the state of the art of drilling and tapping screws: 3,079,831, 3,094,893, 3,125,923, 3,318,182. Over the disclosures of these patents the self-drilling and thread swaging screw of the present invention is believed to be a substantial advancement.

SUMMARY OF THE INVENTION The invention pertains to a screw and method of construction which is believed to be new in the art. The screw body is formed from a length of rod or wire which is shaped in a die under pressure to have a cylinder body with a head on one end, a tapered section and a cylindrical extension on the opposite end. The blank is further formed in a die by inwardly extending flutes forming slides which produce recesses on opposite sides of the body disposed in angular relation on each side of an axial plane extending into the cylindrical extension, the tapered portion and the adjacent portion of the body. Thereafter, the blank is rolled between a pair of threading dies to provide a thread on the body and the tapered end section the latter of which are chambered. The rolling operation deflects the metal of the advancing faces of the thread sections into the flutes and form swaging rather than cutting edges. Thereafter, the end of the cylindrical extensions is ground to have cutting edges which are relieved to provide a drill end on the screw, the grinding operation being performed after a hardening operation. The resulting screw readily cuts a hole in a metal member which is enlarged by the tapered portion until engaged by the cha mfered thread which begins swaging the wall of the enlarged hole to form a thread therein. The swaging of the thread provides a clamping pressure in the Wall of the hole which tightly grips the thread on the screw after the screw is fully driven.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a view in elevation of a screw having threads on the body, a driving head on one end and a drill projection on the opposite end embodying features of the present invention;

FIG. 2 is a view in elevation of a blank which was cold formed and from which the screw of FIG. 1 was fabricated;

FIG. 3 is a broken view of the structure illustrated in FIG. 2, showing structure for forming flutes therein;

FIG. 4 is a view of the structure illustrated in FIG. 3 showing the thread being rolled therein;

FIG. 5 is a view of the structure illustrated in FIG. 4

3,507,183 Patented Apr. 21, 1970 p CC after the thread rolling operation showing the formation of cutting edges on the projecting drill section;

FIG. 6 is a view of the structure illustrated in FIG. 5, as viewed from the left-hand end thereof;

FIG. 7 is a broken view of the structure illustrated in FIG. 5 during a drilling operation in a workpiece;

FIG. 8 is a view of the structure illustrated in FIG. 7 after the drilling and hole enlarging operation and during the swaging of the wall of the resulting aperture to form a thread therein; and

FIG. 9 is an enlarged broken sectional view of the structure illustrated in FIG. 7, taken on the line 9-9 thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT A self-tapping and thread swaging screw 11 illustrated in FIG.1 is shown after a drill end 12 had drilled a hole 13 in a workpiece which was enlarged by a truncated conical section 14 to have a chamfered thread section 15 swage a thread 16 within the hole 13. The swaged thread 16 provides a binding force on a thread 17 on the screw body when the screw is driven to a desired position by a head 18 on the end opposite to that having the drilling point 12 thereon. A blank 21, illustrated in FIG. 2, is formed from a length of wire or rod, in a die having a cylindrical body 22, the drawing head 18, a truncated conical section 24 and a cylindrical end 25. In the same or different die into which the blank is inserted, a pair of oppositely disposed slides 26 having arcuate ends are forced inwardly to form arcuates 27 which may be parallel to the axis of the body 22 but which are illustrated as being disposed on oppositesides of the center line in angular relation to each other.

The flutes 27 extend into the drill head 12, the truncated conical section 14, the chamfered thread 15 on a conical section 23 and the adjacent section of the thread 17. Thereafter, as illustrated in FIG. 4, the body 22 is rolled between upper and lower die plates 28 for rolling the thread section 15 and 17 on the body 22 of the screw. The metal is swaged into the thread of the die and in the tapered portion 23 of the thread sections 29 between the flutes 27, the thread progressively reduces in height toward the drill end 12. In the rolling operation the metal 30 at the forward faces of the thread sections 29 is rolled into the flutes 27 forming swaging rather than cutting edges so that swaging will be performed by the thread sections 29 when the screw is being applied to a workpiece.

The swaging of the flutes, as illustrated in FIG. 3, produces the extension of the end portion 25 and the cold working of the blank raises the tensile strength of the material. When not hardened sufiiiciently, the screws are large its own hole when the screw is being applied to a workpiece.

In FIG. 7, the screw 11 is illustrated as having its drill end 12 starting the hole 13 in the workpiece. In FIG. 8, as the hole is being drilled it is enlarged by the truncated conical section 14 which permits the thread end on the forward end of the truncated section 15 to enter the enlarged aperture and have the thread sections swage the wall thereof to form a thread therein. The thread is engaged by the thread 17 of the screw and is clamped thereon by the binding engagement produced by the swaged thread in the wall of the hole. The angular location of the flutes produces a faster swaging operation than when the flutes are disposed parallel, although parallel flutes could be employed. The hole is drilled by a drill point provided on the end of each screw which requires a grinding operation to produce sharp relieved cutting edges on the end. This is the only machining operation required for the completed screw, the minimal cost of which in high production is well worth the results which is obtained in providing a screw which will drill its own hole as readily as a drill of conventional form.

What is claimed is:

1. In a self-drilling and thread swaging screw, a hardened body having driving means on one end of the body, a truncated conical section with a drill extension on the other end of the body, a like and continuous thread on the body and the truncated section that on the latter being of progressively lesser depth to a lead end, a reamer section between the concal section and drill extension for enlarging the drilled hole, a plurality of generally longitudinal flutes extending in the drill extension, the reamer and conical sections and into the adjacent thread on the bady, the metal on the advancing faces of the thread sections formed by the flutes including the entire cross section of each of the thread ends adjacent the flutes being deflected thereinto so as to be radially relieved with respect to the adjacent portions of the thread for producing swaging ends.

2. In a screw as recited in claim 1 wherein sloping relief cutting edges are formed on the end of the drill extension.

3. In a screw as recited in claim 2, wherein the reamer section has the thread swaging starting end blended thereinto.

4. In a screw as recited in claim 3, wherein said flutes comprise a pair of oppositely located angularly disposed arcuate recesses.

5. In a screw as recited in claim 4, wherein the flutes are angularly disposed relative to each other and to a plane through the axis of the screw.

References Cited UNITED STATES PATENTS 3,094,894 6/1963 Broberg 8547 3,125,923 3/ 1964 Hanneman 8547 3,238,836 3/ 1966 Johnson 8547 3,251,080 5/ 1966 Sharon 10152 RAMON S. BRI'ITS, Primary Examiner US. Cl. X.R. 

